Police investigating the disappearance of Jessica Heeringa have now released a sketch of the man they are looking for, while an eyewitness tells ABC News that another man who approached the gas station attendant the night she vanished was "being real flirty" with her.

An employee at a store adjacent to the gas station saw the 25-year-old mother there only hours before she vanished last Friday night. Christian VanAntwerpen watched a man in a silver minivan approach Heeringa when she was at a gas pump.

"He was just like, 'Hey, what are you doing over here? Aren't you supposed to be inside?' Just kind of being real flirty, weird about it," VanAntwerpen told ABC News.

"It was just bizarre that he seemed to be actively looking for her, like he knew her and then had this attitude that he wanted to have a conversation with her and then conduct business, and that is what seemed really out of place to me," VanAntwerpen said.

VanAntwerpen said that during the Friday night encounter, Heeringa remained calm

"Jessica was always one of those people that even if she was uncomfortable with somebody, she always had a sense of grace," VanAntwerpen said. "You see all sorts of people in retail, and her being in a different kind of retail, you can always sense when somebody is uncomfortable, or this is inconvenient for me. But she always had a sense about her to always be courteous and kind to that person and take care of things."

Newly released surveillance video shows a gray minivan, similar to the van the witness described -- traveling northbound, away from the Norton Shores, Mich., Exxon station, where Heeringa was working alone on the late shift Friday. That gray minivan is now being sought by police in connection with her disappearance.

"It's very frustrating, you know. I want my sister back," Jessica Heeringa's sister, Samantha Heeringa, told ABC News. "But I have hope that she'll be found soon ... Everybody's a wreck and will be until she's found."

Samantha Heeringa was one of hundreds of people gathered for a candlelight vigil tonight in the field across from the gas station where she worked and was last seen.

The driver of the van was described by witnesses as a white male, 6 feet tall with a medium to heavy build, Shaw said. The man was last seen wearing a bright red or orange sweatshirt, according to police.

Police have also released the 911 call from a concerned customer who alerted authorities around 11:15 p.m. Friday after he found the gas station eerily empty.